From the prior art many methods are known to qualitatively or quantitatively investigate the ingredients of agricultural products, in particular grain. In order to figure out the value of a growing, harvested, or stored crop and to decide upon possible actions it is important to know about the ingredients.
Today, samples are taken and sent to specialized laboratories for analysis. Not available so far, however, except for moisture, are rugged and relatively low-cost analyzers for widespread use. The greatest demand is in the analysis of staple foods, i.e., crops that are routinely eaten by many people and that supply one or more of the three organic macronutrients needed for survival and health: carbohydrates, proteins, and fats.
Most staple foods are derived from cereals (for instance wheat, maize, rice) or root vegetables (for instance potato. Other staple foods include legumes (for instance beans or peas) and fruits (for instance apple, tomato, or nuts).
Low cost analyzers are available today only for moisture, where electrical properties of the sample can be measured (capacitance or resistance). In particular, moisture meters for grain are very common. One approach is to measure the change in capacitance of a capacitor into which a grain sample is placed. In U.S. Pat. No. 5,716,272 A the moisture content in grain is measured using this approach.
Optical methods can measure moisture more accurately and can also measure substances other than moisture, for instance, protein. Commonly, infrared light transmissive and reflective methods are utilized. In EP 0 511 184 A1 a reflective method is applied to a sample container with a window, whereas the window is used to obtain a reflective response from the randomly distributed sample elements.
U.S. Pat. No. 6,369,388 B2 discloses a handheld optical analyzer intended for various grains using a similar sample container, which can be placed into a light port for analysis taking into account the transmitted or the reflected near-infrared light (NIR light).
So far the evenly distributed, random deposition of the kernels in the grain sample was crucial in order to achieve a reliable transmitted or reflected response. For similar reasons also the approach of multiple light sources (NIR-LEDs) is used in U.S. Pat. No. 4,286,327 to be able to average over a number of light sources as well. However, the even and random distribution still remains a crucial premise for a reliable analysis.
Generally speaking, when measuring granular samples the transmissive methods bear the problem of accidental background noise originated in unfavorable sample element distributions, whereas the reflective methods bear the problem that only a minimum of the sample mass is taken into account. Most of the inner part of the sample remains hidden inside without having any effect on the spectral light filtering. This effect is not as problematic with transmissive methods, however, there a full absorption may take place due to the thickness of the sample resulting in nearly zero transmission or total absorption leaving no measurable signal.
The mass of the sample that does not contribute to the spectral filtering in one of the scenarios described above will be called “hidden mass” in the following. In many reflective measurements, the bulk of the sample mass is hidden due to the limited light penetration depth underneath the illuminated surface. In transmission measurements, even when performed at only moderate levels of overall absorption, large parts of the mass of a granular sample are often hidden by the fact that the majority of the detected light reaches the detector by sneaking through highly transmissive areas in the sample, such as the air gaps in a grain sample, rather than through the sample mass.
In WO 1999/40419 A1 a technique is disclosed where the sample preparation and preconditioning is optimized for the analysis. The optical analysis is performed on a continuous flow of harvested grain, whereas the analyzing beam is well-defined in space directed on an interaction area inside the sample flow. The optical setup is run in reflectance making sure that only the light with a sample interaction is taken into account. The reflected light contains mainly information on the ingredients in the superficial layer of the grain. The moving flow randomizes and therefore averages over the shape of the kernels and their positioning in respect to the light beam in a convenient way.
However, the problem remains to generate a reasonable randomization of the samples in order not to jeopardize the reliability of the spectrally filtered response. At the same time the optical analyzer itself should have an inexpensive, but reliable setup for measuring the concentration of the sample's ingredients and likewise an optical analyzing method should be easily feasible.